Network Working Group R. Mahy
Request for Comments: 5028 Plantronics
Category: Standards Track October 2007
A Telephone Number Mapping (ENUM) Service Registration forInstant Messaging (IM) Services
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document registers a Telephone Number Mapping (ENUM) service for
Instant Messaging (IM). Specifically, this document focuses on
provisioning 'im:' URIs (Uniform Resource Identifiers) in ENUM.
1. Introduction
ENUM (E.164 Number Mapping, RFC 3761 [1]) is a system that uses DNS
(Domain Name Service, RFC 1034 [2]) to translate telephone numbers,
such as '+12025550100', into URIs (Uniform Resource Identifiers, RFC3986 [3]), such as 'im:user@example.com'. ENUM exists primarily to
facilitate the interconnection of systems that rely on telephone
numbers with those that use URIs to identify resources.
Instant Messaging (IM) is a service defined in RFC 2778 [6] that
allows users to send and receive typically short, often textual
messages in near real-time. The IETF has defined a generic URI used
to identify an IM service for a particular resource: the 'im:' URI
scheme (defined in RFC 3861 [4]). RFC 3861 [4] also defines rules
for discovering service running specific protocols, such as SIP (the
Session Initiation Protocol, RFC 3261 [8]) and XMPP (the eXtensible
Messaging and Presence Protocol, RFC 3921 [9]) from a specific 'im:'
URI.
RFC 3953 [10] already defines an enumservice for presence services,
which returns 'pres:' URIs (also defined in RFC 3861 [4]). This
document registers an enumservice for advertising IM information
associated with an E.164 number.
Mahy Standards Track [Page 1]

RFC 5028 IM Enumservice October 20072. ENUM Service Registration - im
As defined in RFC 3761 [1], the following is a template covering
information needed for the registration of the enumservice specified
in this document:
Enumservice Name:
"im"
Enumservice Type:
"im"
Enumservice Subtypes:
N/A
URI scheme(s):
"im:"
Functional Specification:
This Enumservice indicates that the resource identified is an
'im:' URI. The 'im:' URI scheme does not identify any particular
protocol that will be used to handle instant messaging receipt or
delivery, rather the mechanism in RFC 3861 [4] is used to discover
whether an IM protocol supported by the party querying ENUM is
also supported by the target resource.
Security considerations:
See section 3.
Intended usage:
COMMON
Author:
Rohan Mahy (rohan@ekabal.com)
3. Security Considerations
The Domain Name System (DNS) does not make policy decisions about
which records it provides to a DNS resolver. All DNS records must be
assumed to be available to all inquirers at all times. The
information provided within an ENUM record set must therefore be
considered open to the public -- which is a cause for some privacy
considerations.
Revealing an 'im:' URI by itself is unlikely to introduce many
privacy concerns, although, depending on the structure of the URI, it
might reveal the full name or employer of the target. The use of
anonymous URIs mitigates this risk.
As ENUM uses DNS, which in its current form is an insecure protocol,
there is no mechanism for ensuring that the answer returned to a
query is authentic. An analysis of threats specific to the
dependence of ENUM on the DNS is provided in RFC 3761, and a thorough
analysis of threats to the DNS itself is covered in RFC 3833 [11].
Many of these problems are prevented when the resolver verifies the
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RFC 5028 IM Enumservice October 2007
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